Relay device, program, and display control method

ABSTRACT

A relay device acquires network topology data representing a network topology that includes a connection relationship of each relay device and a connection relationship of a terminal device connected to each relay device in a local area network (LAN), and displays, on a display device, an image of a tree structure in which each relay device included in the LAN corresponds to a node, as an image of the network topology represented by the acquired network topology data. The relay device displays, on the display device, the image of the tree structure in which a node corresponding to a relay device designated in advance among the relay devices included in the LAN and nodes of up to directly below the designated node are set as a drawing target.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No.PCT/JP2015/065954, filed Jun. 2, 2015, which claims priority under 35U.S.C. § 119 from Japanese Patent Application No. 2014-114445, filedJun. 2, 2014, the entire disclosures of which are herein expresslyincorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to supporting the management of theconnection relationship of each communication device in a local areanetwork (LAN).

In a company, for example, a communication system for the whole companyis generally built by connecting the LAN provided in each base such as abranch office or the like to a communication network such as theInternet via a router. This type of LAN includes a terminal device suchas a personal computer that is used by an employee or the like of thecompany, a printer device that is shared by a number of employees, etc.,and a relay device such as a switching hub, a wireless access pointdevice, a router, etc. for connecting the terminal device to the LAN, ascomponents. Hereinafter, the terminal device and the relay device arecollectively referred to as a “communication device” in some cases. Ingeneral, these communication devices are set as an asset managementtarget of the company. For this reason, in the company, in preparationfor accounting or like, detailed information such as the name and theinstallation location of the communication device is generallyregistered and managed in a ledger (or handwritten ledger) created by aspreadsheet software, a database, etc., for each communication device.

In the company, in many cases, a communication device is added, or theinstallation location of a communication device is changed in accordancewith department creation or department reorganization. In this way, in asituation where an addition of a communication device or a change in theinstallation location of a communication device occurs frequently, awork load of the registration to the ledger or the update of theregistered information becomes great, and a delay is likely to occur inthe registration of the detailed information to the ledger or the updateof the registered detailed information. Moreover, there may be a casewhere the registration to the ledger or the update of the registeredinformation is forgotten. When the registration of the detailedinformation to the ledger or the update of the registered detailedinformation is forgotten, a discrepancy between the contents registeredin the ledger and the connection relationship of each communicationdevice in the LAN (also referred to as a network topology) occurs. Inorder to correct the discrepancy, effort is required such as in areinvestigation of the installation location or the connectionrelationship of each communication device, etc. In addition, in themanagement using the ledger, when the installation location of acommunication device is changed without permission, or also when acommunication device that is not permitted is connected to the LAN, adiscrepancy between the contents registered in the ledger and the actualconnection relationship of each communication device in the LAN occurs.That is, in the management using the ledger, even though the ledger isreferred to, it is not always possible to recognize the actual networktopology of the LAN, and especially, in a case where the networktopology can be changed, there is a problem that it is difficult tofollow the changes.

The present invention has been made in consideration of theabove-described problem, and an object thereof is to provide a techniquecapable of easily recognizing the network topology of a LAN that isconnected to a communication network via a relay device, and quicklyrecognizing a changed portion in the network topology when a change inthe network topology occurs.

In order to solve the above-described problem, the present inventionprovides a relay device including: network topology data acquisitionmeans for acquiring network topology data representing a networktopology that includes a connection relationship of each relay deviceand a connection relationship of a terminal device connected to eachrelay device in a local area network (LAN); and display control meansfor displaying, on a display device, an image of a tree structure inwhich each relay device included in the LAN corresponds to a node, as animage of the network topology represented by the network topology dataacquired by the network topology data acquisition means, in which thedisplay control means displays, on the display device, the image of thetree structure in which a node corresponding to a relay devicedesignated in advance among the relay devices included in the LAN andnodes of up to directly below the designated node are set as a drawingtarget. Here, as a response to being given an expansion instruction fora certain node included in the drawing target, the nodes of up todirectly below the node to which the expansion instruction is given maybe set as a new drawing target, and the display contents of the displaydevice may be updated. The expansion instruction for a certain nodeincluded in the drawing target is performed, for example, by anoperation on the image corresponding to the node. As another aspect ofthe present invention, an aspect that provides a program causing ageneral computer such as a central processing unit (CPU) or the like tofunction as the network topology data acquisition means and the displaycontrol means is also considered. Still another aspect of the presentinvention, an aspect that provides a display control method of the relaydevice performing the steps corresponding to the network topology dataacquisition means and the display control means is also considered.

As an example of the network topology data acquisition means, variousaspects may be considered. For example, in a case where the relay deviceincluding the network topology data acquisition means is a router thatconnects the LAN to a communication network such as the Internet or thelike, an aspect in which the network topology data acquisition means isconfigured by combining collecting means for collecting datarepresenting a MAC address table and a MAC address from another relaydevice included in the LAN (a router, a switching hub, a wireless accesspoint device, or the like) and network topology data generation meansfor generating the network topology data by analyzing the data collectedby the collecting means, may be considered. In addition, an aspect inwhich the collecting means and the network topology data generationmeans are further included, in which a communication with a device thatgenerates the network topology data is performed by the operation ofeach of these means, and in which means for receiving the networktopology data from the device is used as network topology dataacquisition means, may be also considered. When connecting the LAN tothe communication network such as the Internet or the like, the routeris an essential element, and the router is caused to perform the networktopology display control. Thus, it is possible to achieve energy savingsand cost savings, compared to an aspect in which a dedicated device forthe display control is separately provided.

As a specific aspect of acquisition of the network topology data by thenetwork topology data acquisition means, an aspect in which the networktopology data is acquired according to a user instruction, an aspect inwhich the network topology data is periodically acquired, an aspect inwhich the network topology data is acquired as a response to beingdetected connection or disconnection of another relay device or anotherterminal device to a certain relay device, or the like, are included.According to the relay device, it is possible to easily recognize thenetwork topology of the devices below the relay device designated inadvance in the LAN, from the image of the tree structure displayed onthe display device. Moreover, the display contents of the display deviceare updated, at any timing instructed by the user, periodically, or as aresponse to being detected the connection or the disconnection ofanother relay device or another terminal device to a certain relaydevice. Thus, the user such as a network administrator, a person incharge of accounting, or the like can quickly and easily recognize achange and a changed portion in the network topology, by viewing achange in the image of the tree structure displayed on the displaydevice using his/her eyes. In a case where a simple network managementprotocol (SNMP) is used, there is a problem that only the connectionrelationship of equipment that supports the SNMP is recognized, or aproblem that a computer which operates as an SNMP manager is newlyrequired. Thus, the technique is different from the present inventionthat does not have these problems.

In addition, according to the present invention, the display controlmeans sets the node corresponding to the relay device that is designatedin advance among the relay devices included in the LAN and the nodes ofup to directly below the node as a drawing target, and displays the treestructure on the display device. As a response to being given anexpansion instruction for a certain node, the display control means setsthe nodes of up to directly below the node to which the expansioninstruction is given as a drawing target, and updates the displaycontents of the display device. Therefore, the following effects areexhibited. That is, as the LAN becomes large, when the whole networktopology of the LAN is collectively displayed, there is a concern thatthe display contents of the display device will become complicated andhard to see. However, according to the present invention, a portion auser wants to recognize in detail can be designated by the user, andthus avoidance of complication of the display contents of the displaydevice and recognition of the details of the network topology can bemade compatible.

In yet another aspect of the disclosure, the relay device includesdetailed information acquisition means for acquiring detailedinformation of each relay device in the LAN and the terminal deviceconnected to each relay device. The display control means displays, onthe display device, the image of the tree structure corresponding to thedrawing target and a list image of the detailed information on the relaydevice and the terminal device that are directly below the designatednode among the nodes included in the tree structure, side by side, andas a response to being given an expansion instruction, the displaycontrol means updates the list image of the detailed information to thelist image of the detailed information on the relay device and theterminal device that are directly below the node to which the expansioninstruction is given. The detailed information may include informationrepresenting at least makers of the relay device and the terminaldevice. According to the aspect, display of the network topology of theportion user wants to recognize in detail, and display of the detailedinformation of each communication device can be made compatible, whileavoiding complication of the display contents of the display device. Forexample, when the terminal device is a server device, informationindicating the operation status of the server device (for example,information representing the load of the server device such as CPUutilization efficiency, communication amount per unit time, or the like)is included in the detailed information, and thus it is possible tomonitor the operation status of the server device. When the serverdevice is crashed, the information related to the server device is notdisplayed, and thus it is also possible to immediately detect the serverdevice being crashed. In addition, the communication amount per unit ofterminal (or communication amount per unit time) is included in thedetailed information, and thus it is possible to monitor the traffic ofeach terminal device. Moreover, it is possible to detect a terminaldevice that performs a fraud behavior such as allowing a large amount oftraffic to pass (a terminal device suspected of virus infection), andthus it is also possible to block the communication of this terminaldevice. In addition, information indicating whether or not anti-virussoftware is installed (in a case where anti-virus software is installed,information indicating the version of a virus scanning definition file)is included in the detailed information. Thus, it is possible to monitorthe presence or absence of the connection of a terminal device that doesnot satisfy a security policy related to virus checking, and it is alsopossible to block the communication of this terminal device.

In a case where the relay device according to the present inventionincludes service providing means for providing a certain service to theterminal device in the LAN according to a known communication protocol(that is, in a case where the relay device according to the presentinvention also functions as a server for providing the service), thedetailed information acquisition means may be caused to acquire thedetailed information from the terminal device by using a communicationsequence according to the well-known communication protocol. Accordingto the aspect, the relay device can acquire the detailed information ofeach terminal device without increasing the traffic of the communicationthat is performed between the relay device according to the presentinvention and each terminal device.

In another aspect, the relay device includes: memory means for storingone or more pieces of reference topology data as a reference for theLAN; comparison means for comparing the network topology represented bythe network topology data acquired by the network topology dataacquisition means, and the network topology represented by the referencetopology data designated by a user among the one or more pieces ofreference topology data; and notification means for notifying adifference in the network topologies, in a case where a comparisonresult indicating that there is a difference in the network topologyrepresented by the network topology data acquired by the networktopology data acquisition means and the network topology represented bythe reference topology data is obtained by the comparison means. Forexample, an aspect in which the node or the leaf corresponding to thedifference between the network topology represented by the referencetopology data and the network topology represented by the networktopology data acquired by the network topology data acquisition means isdisplayed on the image of the tree structure or the list image, in adifferent display form from other nodes or other leaves (changing of thedisplay color or blinking), or an aspect in which a networkadministrator is notified by E-mail (or use of both), may be considered.According to the aspect, the user such as a network administrator or thelike can quickly recognize a change from the network topologyrepresented by the reference topology data. Here, with regard to how togenerate the reference topology data, various aspects may be considered.For example, snapshot means for writing the network topology dataacquired by the network topology data acquisition means in the memorymeans, as the reference topology data, according to a user instruction,may be further provided.

In still another aspect of the disclosure, the comparison means comparesthe network topology represented by the network topology data acquiredby the network topology data acquisition means with the network topologyrepresented by the reference topology data, except for a terminal devicedesignated in advance among the terminal devices included in the LAN.According to the aspect, the terminal device such as a wireless terminaldevice in which connection/disconnection is supposed to occur frequentlyis excluded from a comparison target by the comparison means, and thusit is possible to avoid performing of an unnecessary notification.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of one ormore preferred embodiments when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a diagram of an example communication systemincluding a router according to one or more embodiments of the presentinvention.

FIGS. 2A-2D illustrate diagrams of example MAC address tables stored inswitching hubs according to one or more embodiments of the presentinvention.

FIG. 3 illustrates a block diagram of an example router according to oneor more embodiments of the present invention.

FIG. 4 illustrates a flowchart of a flow of the network topology displayprocess that is performed by a control unit of the router according to acommunication control program according to one or more embodiments ofthe present invention.

FIG. 5 illustrates a diagram of example contents stored in a managementtable stored in a non-volatile memory unit of the router according toone or more embodiments of the present invention.

FIGS. 6A and 6B illustrate diagrams of example images displayed on a webconsole by the router according to one or more embodiments of thepresent invention.

FIG. 7 is another flow chart according to one or more embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The embodiments according to the present invention will be describedwith reference to the drawings.

FIG. 1 is a diagram illustrating a configuration example of acommunication system including a router 10 that is an embodiment of arelay device according to the present invention. The communicationsystem includes the router 10 and a LAN 20. The LAN 20 is, for example,a LAN provided at a branch of a company, and connected to acommunication network 30 such as the Internet or a wide area network(WAN) via the router 10. The router 10 is a relay device for relaying apacket communication that is performed according to a communicationprotocol on a network layer (in this embodiment, internet protocol (IP))between the LAN 20 and the communication network 30. The packet is aunit of transmitting and receiving of data on the network layer, andincludes a header portion and a payload portion. IP addresses of thetransmission source and transmission destination of the packet (atransmission source IP address and a transmission destination IPaddress) are written in the header portion of the packet. The IP addressis a communication address to uniquely identify each of thecommunication devices (in the present embodiment, terminal devices 40 orswitching hubs 50) on the network layer. Moreover, data on a higherlayer is written in the payload portion.

As illustrated in FIG. 1, the LAN 20 includes three switching hubs(switching hubs 50A, 50B and 50C), three terminal devices (terminaldevices 40A, 40B and 40C) that are respectively connected to each of theswitching hubs, and a terminal device 40D connected to the router 10. Asillustrated in FIG. 1, the switching hubs 50A, 50B and 50C are connectedto the router 10 in a cascade. In more detail, the switching hub 50A isconnected to the router 10, and the terminal device 40A and theswitching hub 50B are connected to the switching hub 50A. The terminaldevice 40B and the switching hub 50C are connected to the switching hub50B, and the terminal device 40C is connected to the switching hub 50C.The connection between the router 10 and each of the communicationdevices or the connection between the switching hubs (or terminaldevices) may be wired connection or wireless connection.

Each of the terminal devices 40A, 40B, 40C and 40D is a personalcomputer, for example. These four terminal devices perform packetcommunication according to IP between the terminal device itself andother terminal devices included in the LAN 20 or between the terminaldevice itself and various types of server devices or terminal devicesincluded in the communication network 30. One of these four terminaldevices (in the present embodiment, the terminal device 40D) serves as aweb console for the router 10 (that is, a device for providing varioustypes of user interfaces using a web browser). Hereinafter, in a casewhere there is no need to distinguish each of the four terminal devices,the terminal devices are referred to as “terminal devices 40”. A uniqueIP address is respectively assigned to each of these four terminaldevices and the router 10 in advance. The IP address of the router 10 isstored in advance in each of the four terminal devices 40 as an IPaddress indicating a default gateway. Among these four terminal devices,the other terminal devices other than the terminal device serving as aweb console for the router 10 may be a printer or a web camera. In thepresent embodiment, the terminal device that functions as a web consolefor the router 10 is included in the LAN 20 that is connected to theinternet (communication network 30) via the router 10. However, theterminal device that functions as a web console may be connected to thecommunication network 30. As another example of the terminal device thatfunctions as a web console, a smart phone, a tablet terminal, or thelike may be also considered. The terminal device includes a control unit(for example, CPU), a communication interface unit, a memory unit (forexample, RAM), and a bus that mediates data exchange between thesecomponents. Additionally, the terminal device functioning as a webconsole includes a display unit that functions as a web console and anoperation unit such as a mouse and a keyboard, a touch panel, or thelike.

Each of the switching hubs 50A, 50B and 50C is a communication devicethat performs relay control of data on a data link layer which is aprotocol layer lower than IP. In the present embodiment, since the threeswitching hubs have the same configuration, in a case where there is noneed to distinguish each of the switching hubs, the switching hubs arereferred to as “switching hubs 50”. To perform relay of data on the datalink layer means to perform transmission control of a MAC frame(hereinafter, simply referred to as a “frame”) on the data link layer,the MAC frame being a unit of transmitting and receiving of data. TheMAC addresses of the transmission source and the transmissiondestination of the frame (a transmission source MAC address and atransmission destination MAC address) are written in the header portionof the frame. The MAC address is a communication address for uniquelyidentifying each of the communication devices on the data link layer.The router 10, each of the four terminal devices 40, and each of thefive switching hubs 50 respectively have a unique MAC address. Thepacket transmitted from the transmission source is written in thepayload portion.

The router 10 and the switching hubs 50 respectively have a plurality ofports, and other communication devices are connected to each of theseports. For example, as illustrated in FIG. 1, there is a way by whichthe switching hub 50A is connected to the port number 9 (in FIG. 1,referred to as #9, the same is true for the other port numbers) of therouter 10, and which the terminal device 40D is connected to the portnumber 10 of the router 10. As in a general router or a generalswitching hub, a MAC address table in which the MAC address of each ofthe terminal devices 40 is stored is stored in the router 10 and theswitching hubs 50, the terminal devices 40 being directly or indirectlyvia one or more other switching hubs connected to the port indicated bythe port number of the router 10 or the switching hubs 50, and a portnumber of the router 10 or each of the switching hubs 50 beingassociated with a port number of each port of each of the terminaldevices 40.

For example, it is assumed that the MAC addresses of the terminaldevices 40A, 40B, 40C and 40D are mac-a, mac-b, mac-c and mac-d, thatthe MAC address of the router 10 is mac-r, and that each of thecommunication devices is connected as illustrated in FIG. 1. In thiscase, a MAC address table indicating contents illustrated in FIG. 2A isstored in the switching hub 50A. In the same manner, a MAC address tableindicating contents illustrated in FIG. 2B is stored in the switchinghub 50B, and a MAC address table indicating contents illustrated in FIG.2C is stored in the switching hub 50C, respectively. The router 10 alsoincorporates a switching hub (not illustrated in FIG. 1), and theswitching hub stores a MAC address table indicating contents illustratedin FIG. 2D. A technology in the related art such as an addressresolution protocol (ARP) may be appropriately used for generating theseMAC address tables and updating the contents stored in these MAC addresstables. When a frame is received via any port of the router 10 and eachof the switching hubs 50, the router 10 and each of the switching hubs50 transfer the frame to the port indicating the port number that isassociated with the transmission destination MAC address of the frameand stored in the MAC address table of the router 10 and the switchinghubs 50 themselves. The router 10 and the switching hubs 50 perform sucha process, and thus the frame transmitted from any terminal devicereaches to the destination thereof.

As described above, the router 10 performs relay control of the packettransmitted from the communication network 30 to the LAN 20, and relaycontrol of the packet transmitted from the LAN 20 to the communicationnetwork 30. For example, in a case where the transmission destination IPaddress of the packet received from the communication network 30 is anIP address of any one of the terminal devices 40A, 40B, 40C and 40D, therouter 10 transmits the packet to the LAN 20. In a case where thetransmission destination IP address of the packet is not an IP addressof any one of the terminal devices 40A, 40B, and 40C, the router 10performs a process of transmitting the packet to another routeraccording to the contents stored in a routing table.

In the communication system illustrated in FIG. 1, the router 10performs a process that exhibits significant features of the presentembodiment, and thus it is possible to display an image representingnetwork topology of the LAN 20 (that is, the LAN connected to theinternet 30 via the router 10), on the web console. More specifically,in the present embodiment, as the image representing the networktopology, an image representing physical connection relationship (thatis, physical topology) between the communication devices in the LAN 20is displayed on the web console. Therefore, a person in charge ofaccounting or a network administrator in the company can easilyrecognize the physical topology of the LAN 20 by viewing the imagedisplayed on the web console. Hereinafter, the router 10 that exhibitssignificant features of the present embodiment will be mainly described.

FIG. 3 is a block diagram illustrating a configuration example of therouter 10.

As illustrated in FIG. 3, the router 10 includes a control unit 110, afirst communication interface (hereinafter, simply referred to as “I/F”)unit 120, a second communication I/F unit 130, a memory unit 140, and abus 150 that mediates data exchange between these components.

The control unit 110 is a CPU, for example. The control unit 110functions as a control center of the router 10 by executing acommunication control program 144 a stored in the memory unit 140 (moreprecisely, a non-volatile memory unit 144). The details of the processthat is performed by the control unit 110 according to the communicationcontrol program 144 a will be described later.

All of the first communication I/F unit 120 and the second communicationI/F unit 130 are a network interface card (NIC). The first communicationI/F unit 120 is connected to the LAN 20. More specifically, the firstcommunication I/F unit 120 has a plurality of ports, and the switchinghub 50A and the terminal device 40D are respectively connected todifferent communication ports. The second communication I/F unit 130 isconnected to the communication network 30. The first communication I/Funit 120 and the second communication I/F unit 130 deliver the packetthat is received from a network of each connection destination thereofto the control unit 110. Meanwhile, the first communication I/F unit 120and the second communication I/F unit 130 transfer a packet that isreceived from the control unit 110 to the network of each connectiondestination thereof.

As illustrated in FIG. 3, the memory unit 140 includes a volatile memoryunit 142 and a non-volatile memory unit 144. The volatile memory unit142 is, for example, a random access memory (RAM). The volatile memoryunit 142 functions as a work memory when the communication controlprogram 144 a is executed. Although the details of the volatile memoryunit 142 are not illustrated in FIG. 3, a routing table is stored in thevolatile memory unit 142. The non-volatile memory unit 144 is a flashROM, for example. The communication control program 144 a and amanagement table 144 b are stored in the non-volatile memory unit 144 inadvance.

The control unit 110 reads the communication control program 144 a fromthe non-volatile memory unit 144 to the volatile memory unit 142, andstarts the communication control program 144 a, as a response to beingsupplied power (not illustrated) to the router 10 or being reset therouter 10. The control unit 110 that operates according to thecommunication control program 144 a performs a packet relay process anda network topology display process. Among these two processes that areperformed by the control unit 110 according to the communication controlprogram 144 a, the packet relay process is the same as that of a generalrouter, and thus the detailed description thereof will be omitted.Hereinafter, the network topology display process will be mainlydescribed.

The network topology display process is a process that is periodicallyperformed at constant intervals. In this network topology displayprocess, the control unit 110 functions as network topology dataacquisition means, detailed information acquisition means, and displaycontrol means in FIG. 3. In other words, the communication controlprogram 144 a according to the present embodiment is a program thatcauses the control unit 110 to function as the network topology dataacquisition means, the detailed information acquisition means, and thedisplay control means. FIG. 4 is a flowchart illustrating a flow of thenetwork topology display process. As illustrated in FIG. 4, the networktopology display process includes a collection process SA100, a networktopology data generation process SA110, a detailed informationacquisition process SA120, and a display control process SA130. Asillustrated in FIG. 4, the network topology data acquisition meansperforms the collection process SA100 and the network topology datageneration process SA110, the detailed information acquisition meansperforms the detailed information acquisition process SA120, and thedisplay control means performs the display control process SA130. Thecontents of these four processes included in the network topologydisplay process are as follows.

The collection process SA100 is a process of communicating with each ofthe switching hubs included in the LAN 20, and collecting datarepresenting the contents stored in the MAC address table of each of theswitching hubs and the MAC address of each of the switching hubs (aframe in which the MAC address table is written in the payload portionthereof; hereinafter, referred to as a MAC address table reply frame)from each of the switching hubs. For example, it is considered that thecontrol unit 110 writes a multicast address and the MAC address of therouter 10 in the transmission destination address and the transmissionsource address of the header portion, transfers a frame in which acommand for instructing the transmission of the MAC address table replyframe is written in the payload portion to the LAN 20, and causes eachof the switching hubs 50 to perform a process of replying the MACaddress table reply frame as a response to being received the frame.

The network topology data generation process SA110 that is performedsubsequent to the collection process SA100 is a process of analyzingdata collected from each of the switching hubs by the collection processSA100, generating network topology data representing the networktopology of the LAN 20, and writing the network topology data in thevolatile memory unit 142. In the present embodiment, as the networktopology data, data representing a tree structure in which the router 10is corresponded to a root, each of the switching hubs 50 is correspondedto a node (knob), and each of the terminal devices 40 is corresponded toa leaf, is used. The root is at the top level (the uppermost) of thetree structure, and normally, only one root exists in a single treestructure. The leaf is the end of the tree structure, and the node meansneither the root nor the leaf in the tree structure. As the datarepresenting the tree structure, a set of the structure that correspondsto each of the root, the node, and the leaf may be used, the set of thestructure including a data region that stores a identifier indicatingeach of the devices corresponding to the structure (for example, the MACaddress of the device), an upstream-side pointer indicating one deviceat upstream side (root side), and a downstream-side pointer indicatingone device at downstream side.

For example, in the collection process SA100, it is assumed that thedata representing each of the MAC address tables in FIGS. 2A to 2C iscollected from each of the switching hubs 50A to 50C, and that the MACaddress table in FIG. 2D is stored in the switching hub incorporated inthe router 10. First, the control unit 110 detects that the terminaldevice having the MAC address of mac-d (that is, the terminal device40D) is directly connected to the router 10 itself, with reference toeach of the MAC address tables. The terminal device having the MACaddress of mac-d can be specified as being directly connected to therouter 10 itself, because the MAC address does not appear in other MACaddress tables other than that of the router 10 itself. The control unit110 stores NULL in an upstream-side pointer of the structure thatcorresponds to the router 10, and stores the address of the structurethat corresponds to the terminal device 40D in one downstream-sidepointer of the structure. Then, the control unit 110 stores the addressof the structure that corresponds to the router 10 in the upstream-sidepointer of the structure that corresponds to the terminal device 40D,and stores NULL in the downstream-side pointer of the structure.

Then, the control unit 110 specifies the switching hub that is directlyconnected to the router 10 itself. In the example illustrated in FIGS.2A to 2D, the control unit 110 specifies the switching hub 50A as theswitching hub that is directly connected to the router 10 itself, anddetects that the terminal device having the MAC address of mac-a (thatis, terminal device 40A) is directly connected to the switching hub 50Awith reference to the MAC address table (FIG. 2A) collected from theswitching hub 50A. The control unit 110 stores the address of thestructure corresponding to the switching hub 50A in one downstream-sidepointer in which a value is not set, among downstream-side pointers ofthe structure corresponding to the router 10. Then, the control unit 110stores the address of the structure corresponding to the router 10 inthe upstream-side pointer of the structure corresponding to theswitching hub 50A.

Next, the control unit 110 specifies the switching hub having a port towhich the MAC address of the router 10 itself and the MAC address of theterminal device that is directly connected to the switching hub that isdirectly connected to the router 10 itself (hereinafter, referred to asa first stage switching hub) are associated with each other, as a secondstage switching hub when viewed from the router 10 itself. Hereinafter,in the same manner, the control unit 110 specifies the switching hubhaving a port to which the MAC address of the router 10 itself, the MACaddress of the terminal device that is directly connected to the firststage switching hub, and the MAC address of the terminal device that isdirectly connected to the second stage switching hub are associated witheach other, as a third stage switching hub when viewed from the router10 itself. In this way, the switching hub of each stage that isconnected to the router 10 in a cascade, and the terminal device that isdirectly connected to the switching hub are specified, and the networktopology of the LAN 20 is specified. The control unit 110 updates thevalue of each of the upstream-side pointers and the downstream-sidepointers of the structure, based on the specified result, and thus thenetwork topology data is completed.

The detailed information acquisition process SA120 is a process ofsearching for the management table 144 b using the MAC address of thecommunication device corresponding to each node and each leaf in thetree structure as a search key, and acquiring detailed information onthe communication device. FIG. 5 is a diagram illustrating an example ofthe contents stored in the management table 144 b. As illustrated inFIG. 5, the detailed information on the communication device is storedin advance in the management table 144 b as being associated with theMAC address of the communication device included in the LAN 20. Asillustrated in FIG. 5, although the detailed information according tothe present embodiment includes a host name (in a case of a relay devicesuch as a switching hub, a device name), a terminal type, a maker name,a model name, a type or name of an operating system (OS), the IPaddress, and information representing a comment (for example, characterstring information), the information constituting the detail informationis not limited thereto.

For example, the detailed information on a personal computer may includea type or name of virus checking software installed on the personalcomputer, and information representing a version of a virus scandefinition file. In the detailed information acquisition process SA120,the control unit 110 searches for the management table 144 b using theMAC address represented by each of the data collected in the collectionprocess and each of the MAC address stored in the MAC address tablerepresented by the data as a search key, and reads the detailedinformation that is stored in the management table 144 b as beingassociated with the same MAC address as the search key.

The display control process SA130 is a process of displaying an image ofthe tree structure representing the connection relationship of eachrelay device in the LAN (that is, in the present embodiment, the LAN 20)on the web console according to the network topology data generated inthe network topology data generation process SA110. The network topologyof the LAN is represented by the network topology data. In the presentembodiment, the feature of the present invention appears in a displayform of the image representing the tree structure. More specifically,the control unit 110 sets the nodes of up to directly below the nodecorresponding to the relay device that is designated in advance by theuser (hereinafter, referred to as a drawing start point) among the relaydevices included in the LAN (that is, directly connected to the drawingstart point), as a drawing target, and displays the image of the treestructure up to the drawing target and the image of the list of thedetailed information on the node and the leaf that are directly belowthe drawing start point, in parallel, on the web console. In the presentembodiment, the relay device that connects the LAN 20 to thecommunication network 30 (the relay device at the most upstream in theLAN 20, that is, the router 10) is designated in advance by a user, asthe drawing start point. Therefore, the image illustrated in FIG. 6A isdisplayed on the web console.

More specifically, as illustrated in FIG. 6A, the control unit 110displays the image of the tree structure on a first display area A01 byassigning character string information representing a device name amongthe detailed information to the icon representing each of the drawingstart point (the router 10) and the node directly below the drawingstart point. The control unit 110 displays the list of the detailedinformation on the node and the leaf that are directly below the drawingstart point, on a second display area A02 adjacent to the first displayarea A01 on the right side. In a case where the sufficient width todisplay each information included in the detailed information cannot beassigned in the second display area A02, as illustrated in FIG. 6A, ascroll bar A03 to horizontally scroll the display contents of the seconddisplay area may be provided. In the same manner, in a case where thelongitudinal width is not sufficient, a scroll bar to longitudinallyscroll the display contents of the second display area may be provided,and this is the same for the first display area A01. Additionally, inthe example illustrated in FIG. 6A, although a rectangular shape icon isused as an icon representing the node, and a circular shape icon is usedas an icon representing the leaf, other shape icons may be used. Forexample, the icon representing a directory by a folder in the filemanager of explorer or X window system may be used as an iconrepresenting the node, and the icon representing a file may be used asan icon representing the leaf.

The user who views the image illustrated in FIG. 6A can give anexpansion instruction of the tree structure lower than the node byspecifying the icon of any node among the icons displayed in the firstdisplay area A01 or the second display area A02 with a mouse click, atouch operation, or the like. As a response to being given the expansioninstruction for the node via the web console, the control unit 110 setsthe nodes of up to directly below the node to which the expansioninstruction is given as a drawing target, and updates the displaycontents of the web console. In the present embodiment, the userdesignates the icon of the node directly below the router 10 (that is,the node corresponding to the switching hub 50A) with a mouse click, andthus the nodes of up to directly below the node are set as a drawingtarget and the first display area A01 is updated. Then, in the presentembodiment, the control unit 110 updates the display contents of thesecond display area A02 with an image of the list of the detailedinformation on the node and the leaf directly below the node to whichthe expansion instruction is given, in accordance with updating of thedisplay contents of the first display area A01. As a result, the displaycontents of the first display area A01 and the second display area A02on the display screen of the web console are updated as illustrated inFIG. 6B. In the screen illustrated in FIG. 6A or FIG. 6B, instead ofupdating the display contents of the second display area A02 byspecifying a triangle-shaped icon given in front of the icon indicatinga node in the first display area A01 with a mouse click or the like, itis possible to display again the image of the tree structure by settingthe nodes of up to directly below the node in the first display area A01as a drawing target.

In this configuration, according to the present embodiment, it ispossible to easily recognize the network topology of the LAN 20 byviewing the image of the tree structure displayed on the display deviceof the terminal device 40D serving as the web console for the router 10.In addition, according to the present embodiment, the user can recognizethe network topology of the LAN 20 by designating a portion user wantsto recognize in detail in the network topology of the LAN 20. In thepresent embodiment, although a case where the relay device at the mostupstream of the LAN 20 is designated in advance as a drawing start pointis described, another relay device (that is, any one of the switchinghubs 50A to 50C) may be designated. In addition, according to thepresent embodiment, the network topology display process is periodicallyperformed at constant intervals. Thus, when the change in the networktopology occurs, it is possible to quickly recognize the changedportion.

According to the present embodiment, the image representing the networktopology is displayed according to the stored contents of the MACaddress table that is stored in each of the switching hubs 50.Therefore, even in a case where a communication device that performscommunication without passing through the router 10 (terminal device orthe like that only communicates with another terminal device connectedto each of the switching hubs 50 that is the connection destination ofthe terminal device itself) is included in the LAN 20, it is possible todisplay the image of the network topology including the communicationdevice on the web console.

As described above, although one embodiment of the present invention hasbeen described, the following additional embodiments and/ormodifications may be naturally added to the embodiment.

In one embodiment, although a case where the relay device under thecontrol of the router 10 (relay device included in the LAN that isconnected to the communication network 30 via the router 10) is aswitching hub has been described, the relay device under the control ofthe router 10 may be a router or a wireless access point device. In theabove embodiment, the image of the tree structure representing thephysical connection relationship (physical topology) of each of therelay devices in the LAN 20 connected to the communication network 30via the router 10 is displayed on the terminal device that functions asthe web console of the router 10. However, the image of the treestructure representing the logical connection relationship (virtuallocal area network (VLAN) group; hereinafter, referred to as a logicaltopology) of each of the relay devices in the LAN 20 may be displayed onthe terminal device that functions as the web console of the router 10.The VLAN means a virtual network formed by grouping communicationdevices belonging to the LAN according to the port, the MAC address, andthe communication protocol of the relay device such as the switchinghub, and the VLAN group means each group obtained by the grouping. Thelogical topology is not limited to the VLAN group, and may be aconnection relationship focusing on the flow of data. The point is, anaspect in which the image of the tree structure representing the networktopology of the LAN 20 is displayed on the terminal device functioningas the web console the router 10 may be provided. The network topologyto be displayed may be a physical topology or a logical topology. Thenetwork topology to be displayed also may be switched between thephysical topology and the logical topology according to the instructionof the user, or the like.

In another embodiment, an application example to the router according tothe present invention has been described. This is because the router isan essential element when connecting the LAN to the WAN such asInternet, and the network topology display process is performed by therouter. Therefore, in a case where SNMP is used, it is unnecessary toseparately provide a dedicated device such as a SNMP manager, and thusit is possible to achieve energy saving and cost saving. However, therelay device to which the present invention is applied is not limited tothe router, and the present invention may be applied to a switching hubor a wireless access point device under the control of the router. Forexample, in a case where the present invention is applied to a switchinghub, the specification of the network topology and the display of thespecification results may be performed on a set of another terminaldevice and another relay device (a switching hub or a wireless accesspoint device) that are directly or indirectly connected to thedownstream of the switching hub (the opposite side of the router).Moreover, the detailed information acquisition process SA120 accordingto the embodiment is not necessarily essential, and may be omitted. Thisis because even though the detailed information acquisition processSA120 is omitted, the image of the tree structure representing thenetwork topology can be displayed. In a case where the detailedinformation acquisition process SA120 is omitted, as an identifier to beassigned to each icon in the tree structure, the MAC address of thedevice corresponding to the icon may be used. Additionally, in theembodiment, the display control of the image representing the networktopology of the LAN 20 is performed by the router 10 that connects theLAN 20 to the communication network 30. However, the display control ofthe image representing the network topology of another LAN differentfrom the LAN 20 can be also performed by the router 10. The point is, aslong as the router 10 can collect the data representing the contentsstored in the MAC address table from each relay device included in theLAN, each relay device being as a display control target of the imagerepresenting the network topology, it is not necessary that the router10 is directly connected to the LAN. Even in a case where the router 10is not connected to the LAN as a target of the display control of theimage representing the network topology, among the relay devicesincluded in the LAN, the relay device designated in advance by the useris set as a drawing start point, and the nodes of up to directly belowthe drawing start point are set as a drawing target. Thus, the displaycontrol of the image representing the tree structure may be started.

In yet another embodiment, an aspect in which the contents stored in theMAC address table of each of the switching hubs 50 are periodicallycollected has been described. However, an aspect in which the contentsstored in the MAC address table are collected according to the userinstruction given via the web console may be adopted. According to theaspect, the network topology data can be generated at any timing, andthus it is possible to perform the display of the image representing thenetwork topology. Moreover, an aspect in which the contents stored inthe MAC address table are collected as a response to being detected theconnection (link-up) or the disconnection (link-down) of the terminaldevices 40 or other switching hubs 50 to each of the switching hubs 50may be adopted. In the same manner, an aspect in which the contentsstored in the MAC address table are collected as a response to beingdetected the connection (link-up) or the disconnection (link-down) ofthe terminal devices 40 or the switching hubs 50 to the router 10 may beadopted. This is because when the connection or the disconnection of theterminal devices 40 or the switching hubs 50 occurs, the change of thenetwork topology always occurs. For the detection of link-up andlink-down of the terminal devices 40 to the switching hubs 50, awell-known technique may be appropriately used. The aspects may be usedin combination of all or two of the aspect in which the contents storedin the MAC address table of each of the switching hubs 50 areperiodically collected, the aspect in which the contents stored in theMAC address table are collected as a response to being detected theconnection (link-up) or the disconnection (link-down) of the terminaldevices 40 to the switching hubs 50, and the aspect in which thecontents stored in the MAC address table are collected according to theuser instruction.

In a further embodiment, the detailed information on each communicationdevice included in the LAN 20 is stored in advance in the managementtable 144 b. However, the detailed information may be updated oradditionally registered by the input operation on the second displayarea A02 of the screen illustrated in FIG. 6A or FIG. 6B. In addition,there is no need to store the management table 144 b in the non-volatilememory unit 144 of the router 10, and the management table 144 b may bestored in another device as long as the management table 144 b is freelyaccessible by the control unit 110 during performing of the detailedinformation acquisition process SA120. Moreover, the contents stored inthe management table 144 b may be output as a file such as a CSV formatfile, and the file may be input to another device. In contrast, a CSVformat file generated by another device may be imported as themanagement table 144 b. For example, when another device is an assetmanagement database server or the like, it is possible to cooperate withan asset management system. When another device is another routerinstalled in the company (a router having the same configuration as therouter 10), single management table can be repeatedly used between therouters. When the detailed information can be acquired by thecommunication between the router and the switching hubs 50 or betweenthe router and the terminal devices 40, there is no need to use themanagement table 144 b. The maker of each communication device can bespecified from the MAC address of the communication device, and thusinformation representing at least makers can be acquired as the detailedinformation.

In a case where the relay device according to the present inventionincludes service providing means for providing a certain service to theterminal device according to a well-known communication protocol (thatis, in a case where the relay device has a certain server function), thedetailed information may be acquired from the terminal device using thecommunication according to the communication protocol. For example, in acase where a dynamic host configuration protocol (DHCP) is used forassigning an IP address to the terminal device and the relay deviceaccording to the present invention has a DHCP server function, thedetailed information of the terminal device is acquired by using a DHCPmechanism. More specifically, a DISCOVER message in which the detailedinformation such as the host name (device name) or the used class (OS)name of the terminal device is given as an option is transmitted to theterminal device to which the IP address is assigned using the DHCP.Here, the DISCOVER message is a communication message requesting theDHCP server to initiate a communication sequence for assigning the IPaddress using the DHCP. When the DISCOVER message is received, the relaydevice acquires the detailed information that is given as an option inthe DISCOVER message, and transmits an OFER message to the transmissionsource of the DISCOVER message according to the DHCP. The managementtable 144 b may be generated by writing the detailed informationacquired by the procedure in the memory unit 140 by being associatedwith the MAC address of the transmission source of the DISCOVER message(or the contents stored in the management table 144 b that depend on thedetailed information may be updated). In addition, the service providedby the service providing means (or the communication protocol to realizethe service providing) is not limited to the DHCP. For example, in thecase of a domain name service (DNS) is used as the communicationprotocol to realize the service (that is, in a case where the relaydevice according to the present invention also serves as a DNS server),an option region for giving the detailed information of the terminaldevice may be provided in the communication message of the DNS, and theterminal device may transmit the communication message in which thedetailed information of the terminal device itself is written in theoption region. The relay device may acquire the detailed information byreading the detailed information written in the option region. Accordingto the aspect, the relay device can acquire the detailed information ofeach terminal device without increasing the traffic of the communicationperformed between the relay device according to the present inventionand the terminal device.

In another aspect, reference topology data representing the networktopology as a reference for the LAN 20 may be stored in the memory unit140 (more specifically, the non-volatile memory unit 144), and asillustrated in FIG. 7, the control unit 110 may be caused to perform acomparison process SB100 for comparing the network topology representedby the reference topology data and the network topology represented bythe network topology data generated by the last network topology datageneration process SA110, and a notification process SB110 for notifyinga difference in both topologies in a case where there is a difference inboth topologies (that is, the control unit 110 may be caused to functionas comparison means for performing the comparison process SB100 andnotification means for performing the notification process SB110). Asidefrom the network topology display process illustrated in FIG. 4, thecontrol unit 110 may be caused to perform the comparison process SB100and the notification process SB110, as a response to being given anexpansion instruction via the web console from the user. Moreover, in acase where the setting to perform the comparison process SB100 and thenotification process SB110 is made, the control unit 110 may be causedto perform the comparison process SB100 and the notification processSB110 in parallel with the network topology display process illustratedin FIG. 4. As a notification form of the difference in the notificationprocess SB110, a form in which the node or the leaf corresponding to thedifference between the network topology represented by the referencetopology data and the network topology represented by the networktopology data is displayed on the image of the tree structure or thelist image in a different display form from other nodes or leaves(changing of the display color or blinking), or a form by which an mailor the like to notify the difference may be transmitted to a networkadministrator, may be considered. In addition, the control unit 110 maybe caused to perform a process of writing the information representingthe node or the leaf corresponding to the difference in the non-volatilememory unit 144, every time the difference is detected in the comparisonprocess SB100.

According to the aspect, in a case where the terminal devices 40 thatare included in the network topology represented by the referencetopology data are not represented in the network topology represented bythe network topology data generated by the last network topology datageneration process SA110, in contrast, in a case where the terminaldevices 40 that are not included in the network topology represented bythe reference topology data are represented in the network topologyrepresented by the network topology data generated by the last networktopology data generation process SA110, the notification is performed.In the former case, it means that the terminal device to be originallyconnected to the LAN 20 is not connected to the LAN 20. When theinformation representing the installation department or the installationlocation of each terminal device is included in the detailedinformation, in a case where the notification in the former case isperformed, it is confirmed that whether or not there is a reasonablereason for that the connection is not detected such as disconnection ofthe power supply of the terminal device, by inquiring of theinstallation department of the terminal device the reason. Thus, it ispossible to quickly respond in a case where a failure of the terminaldevice or a theft occurs. On the other hand, in the latter case, theentry of the terminal device as personal belongings is considered, andthus it is possible to quickly respond to entry of personal belongingsor the like by inquiring of the department. In addition, it isconsidered that the link-up or the link-down of a specific terminaldevice is detected by using the network topology represented by thereference topology data as a reference, and the user such as the networkadministrator is notified by mail or the like.

Here, as a specific generation aspect of the reference topology data,various aspects are considered. For example, an aspect in which thecontrol unit 110 is caused to function as snapshot means for storing thenetwork topology data representing the network topology at the timing ofacquiring the instruction as the reference topology data as a responseto being given an instruction to generate the reference topology datavia the web console (for example, a setting button provided in the webconsole is pressed), is considered. The number of the reference topologydata stored in the memory unit 140 is not limited to one. A plurality ofthe reference topology data representing each different network topologymay be stored in memory unit 140, and the reference topology data as areference in the comparison process may be selected by the user from theplurality of the reference topology data. For example, the user such asa network administrator or the like can switch the content to bedetected according to the time zone, by selectively using the referencetopology data for night time at which there is no employees and thereference topology data for office time at which the terminal devices 40are used by employees.

Moreover, the comparison process may be performed except the terminaldevice designated in advance by the user among terminal devices 40included in the LAN 20. According to this aspect, the terminal devices40 such as a wireless terminal device in which connection/disconnectionis supposed to occur frequently are excluded from a comparison target,and thus it is possible to avoid performing of an unnecessarynotification.

In yet a further embodiment, the communication control program 144 acausing the control unit 110 of the router 10 to perform the networktopology display process which exhibits significant features of thepresent invention is stored in advance in the non-volatile memory unit144 of the router 10. However, the communication control program 144 amay be distributed by being written in computer-readable recordingmedium such as a compact disk-read only memory (CD-ROM) or the like, ormay be distributed by downloading via an electrical communication linesuch as the Internet or the like. The control unit of a general relaydevice such as a router is operated according to the program distributedin the manner, and thus the relay device can function as the relaydevice according to the present invention. In addition, it is consideredthat a program causing the CPU to function as the network topology dataacquisition means and the display control means according to theembodiment is installed in a personal computer or the like, and that thepersonal computer is caused to function as a network topology displaydevice.

The following is a list of reference numerals and correspondingfeatures. 10: router, 110: control unit, 120: first communication I/Funit, 130: second communication I/F unit, 140: memory unit, 142:volatile memory unit, 144: non-volatile memory unit, 144 a:communication control program, 144 b: management table, 150: bus, 20:LAN, 30: communication network, 40, 40A, 40B, 40C, 40D: terminal device,50, 50A, 50B, 50C: switching hub

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. A relay device for connecting to a displaydevice, the relay device comprising: a processor and a memory storinginstructions, the processor executing the stored instructions to:acquire network topology data representing a network topology thatincludes a connection relationship of each relay device of a pluralityof relay devices and a connection relationship of a terminal deviceconnected to each relay device in a local area network (LAN); generate atree structure in which each relay device included in the LANcorresponds to a node and each terminal device included in the LANcorresponds to a leaf; store, in the memory, one node designated inadvance among the relay devices included in the LAN; and display, on thedisplay device, only a partial image of the tree structure in which thedesignated and stored node in advance and nodes of up to directly belowthe designated and stored node are set as a drawing target withoutdisplaying the leaf.
 2. The relay device according to claim 1, wherein,as a response to being given an expansion instruction for a certain nodeincluded in the drawing target, the processor further executes thestored instructions to display contents of the display device by settingnodes of up to directly below the node to which the expansioninstruction is given as a new drawing target.
 3. The relay deviceaccording to claim 2, wherein the processor further executes the storedinstructions to: acquire detailed information of each relay device inthe LAN and the terminal device connected to each relay device; display,on the display device, the image of the tree structure corresponding tothe drawing target and a list image of the detailed information on therelay device and the terminal device that are directly below thedesignated node among the nodes included in the tree structure, side byside; and as a response to being given the expansion instruction, updatethe list image of the detailed information to a new list image of thedetailed information on the relay device and the terminal device thatare directly below the node to which the expansion instruction is given.4. The relay device according to claim 3, wherein the detailedinformation includes information representing at least makers of therelay device and the terminal device.
 5. The relay device according toclaim 1, wherein the processor further executes the stored instructionsto acquire the network topology data, according to a user instruction,periodically, or as a response to being detected connection ordisconnection of another relay device or another terminal device to acertain relay device.
 6. The relay device according to claim 1, furthercomprising: a memory area for storing one or more pieces of referencetopology data as a reference for the LAN, wherein the processor furtherexecutes the stored instructions to: compare the network topologyrepresented by the acquired network topology data, and the networktopology represented by the reference topology data designated by a useramong the one or more pieces of reference topology data; and notify adifference in the network topologies, in a case where a comparisonresult indicating that there is a difference in the network topologyrepresented by the acquired network topology data and the networktopology represented by the reference topology data is obtained bycomparison.
 7. The relay device according to claim 6, wherein theprocessor further executes the stored instructions to: write theacquired network topology data in the memory area, as the referencetopology data, according to a user instruction.
 8. The relay deviceaccording to claim 6, wherein the processor executes the storedinstructions to compare the network topology represented by the acquirednetwork topology data with the network topology represented by thereference topology data, except for a terminal device designated inadvance among the terminal devices included in the LAN.
 9. The relaydevice according to claim 2, wherein the expansion instruction for acertain node included in the drawing target is performed by an operationon the image corresponding to the certain node.
 10. A non-transitorycomputer-readable medium storing instructions, the instructions whenexecuted by at least one processor performs a method comprising:acquiring network topology data representing a network topology thatincludes a connection relationship of each relay device of a pluralityof relay devices and a connection relationship of a terminal deviceconnected to each relay device in a local area network (LAN); generatinga tree structure in which each relay device included in the LANcorresponds to a node and each terminal device included in the LANcorresponds to a leaf; storing, in a memory, one node designated inadvance among the relay devices included in the LAN; and displaying, ona display device, only a partial image of a tree structure in which thedesignated and stored node in advance and nodes of up to directly belowthe designated and stored node are set as a drawing target withoutdisplaying the leaf.
 11. A display control method of a relay device forconnecting to a display device, the method comprising: acquiring networktopology data representing a network topology that includes a connectionrelationship of each relay device of a plurality of relay devices and aconnection relationship of a terminal device connected to each relaydevice in a local area network (LAN); generating a tree structure inwhich each relay device included in the LAN corresponds to a node andeach terminal device included in the LAN corresponds to a leaf; storing,in a memory, one node designated in advance among the relay devicesincluded in the LAN; and displaying, on the display device, only apartial image of a tree structure in which the designated and storednode in advance and nodes of up to directly below the designated andstored node are set as a drawing target, based on the acquired networktopology data, without displaying the leaf.
 12. The method according toclaim 11, wherein, as a response to being given an expansion instructionfor a certain node included in the drawing target, contents of thedisplay device are displayed by setting nodes of up to directly belowthe node to which the expansion instruction is given as a new drawingtarget.
 13. The method according to claim 12, further comprising:acquiring detailed information of each relay device in the LAN and theterminal device connected to each relay device; displaying, on thedisplay device, the image of the tree structure corresponding to thedrawing target and a list image of the detailed information on the relaydevice and the terminal device that are directly below the designatednode among the nodes included in the tree structure, side by side; andas a response to being given the expansion instruction, updating thelist image of the detailed information to a new list image of thedetailed information on the relay device and the terminal device thatare directly below the node to which the expansion instruction is given.14. The method according to claim 13, wherein the detailed informationincludes information representing at least makers of the relay deviceand the terminal device.
 15. The method according to claim 11, whereinthe network topology data is acquired according to a user instruction,periodically, or as a response to being detected connection ordisconnection of another relay device or another terminal device to acertain relay device.
 16. The method according to claim 11, furthercomprising: storing one or more pieces of reference topology data as areference for the LAN; comparing the network topology represented by theacquired network topology data, and the network topology represented bythe reference topology data designated by a user among the one or morepieces of reference topology data; and notifying a difference in thenetwork topologies, in a case where a comparison result indicating thatthere is a difference in the network topology represented by theacquired network topology data and the network topology represented bythe reference topology data is obtained by comparison.
 17. The methodaccording to claim 16, further comprising: writing the acquired networktopology data in the memory area, as the reference topology data,according to a user instruction.
 18. The method according to claim 16,the network topology represented by the acquired network topology datais compared with the network topology represented by the referencetopology data, except for a terminal device designated in advance amongthe terminal devices included in the LAN.
 19. The method according toclaim 12, wherein the expansion instruction for a certain node includedin the drawing target is performed by an operation on the imagecorresponding to the certain node.
 20. The relay device according toclaim 1, wherein the processor further executes the stored instructionsto: acquire detailed information of each relay device in the LAN and theterminal device connected to each relay device; and display, on thedisplay device, the partial image of the tree structure and a list imageof the detailed information side by side, wherein the list image of thedetailed information includes the relay device and the terminal devicethat are directly below the designated and stored node among the nodesincluded in the tree structure.
 21. The relay device according to claim1, further comprising: a plurality of ports for connecting to othercommunication devices; and a first MAC address table in which MACaddresses of the terminal devices are stored in association withcorresponding port numbers of the plurality of ports connected to theterminal devices via one or more relay devices or without any relaydevices, wherein the processor further executes the stored instructionsto: collect, from each relay device, a second MAC address table in whichMAC addresses of the terminal devices are stored in association withcorresponding port numbers of the plurality of ports connected to theterminal devices via one or more relay devices or without any relaydevices; and acquire the network topology data by specifying a relaydevice located at a downstream side of the relay device based on thefirst MAC address table of the relay device and the second MAC addresstable of each relay device.
 22. The relay device according to claim 1,wherein the relay device is a router.
 23. The relay device according toclaim 1, wherein the relay device is a switching hub.